Method and apparatus for backfilling and underpinning an underground coal or ore mine



Apnl 29, 1969 T. J. ooouu 3,

METHOD AND APPARATUS FOR BACKFILLING AND UNDERPINNING AN UNDERGROUND COAL OR ORE MINE Filed May 16, 1967 FIG] ' INVEN'I'OR I g um I k I THOMAS J. DOOLlN M EM, Z4 4 MM ATTORNEYS United States Patent METHOD AND APPAirATUs FOR BACKFILLING AND UNDERPINNING AN UNDERGROUND COAL 0R ORE MINE ABSTRACT OF THE DISCLOSURE The method of filling an inaccessable mine cavity area requires the drilling of at least two holes from the surface into the inaccessable mine cavity. A slurry of solid material and water is pumped downwardly through a conduit inserted in one of the holes and directed towards the other hole within the cavity by means of a variable direction nozzle attached to the lower end of the conduit and extending into the cavity. The excess water is pumped out-; wardly through a conduit in the other bore hole to create a current between the two bore holes to assist in distributing the solid material within the mine cavity.

This invention relates to a method of filling the mine cavity area from which coal or other type material has been removed and the apparatus utilized in the filling operation.

Surface subsidence is a natural and largely unavoidable sequence to underground mine operations by which the minerals from one or more bed 01 veins are extracted. Where pillars have been left in place to support the overlying strata, such support must still be considered to be only of a temporary nature, as nature will not allow manmade voids in the strata to remain open indefinitely. Collapse of such pillars and subsequent subsidence of the overlying strata will result from gradual deterioration, caused by moisture, constant load pressure, and in some instances, from the effect of earth movements in other parts of the mine.

Since surface subsidence can only occur where underground voids exit, it follows logically that surface subsidences may be forestalled or any incipient subsidence minimized in magnitude by filling existing voids in the area.

The practice of backfilling existing underground mine voids in the anthracite region and elsewhere is known as flushing, denoting the transport of solids to be used for backfilling by water through pipelines. When underground voids, especially old mine chambers, are accessible for inspection, as well as for the conduct of backfilling operations, the suitable method of work to be employed is termed controlled flushing. This term denotes that the pipelines can be conducted directly to the chambers and gangways to be backfilled, and brattices or bulkheads can be erected in chambers to confine the backfill material in the space to be backfilled and tightly packed; but where mine workings to be backfilled are not accessible or cannot be made accessible, either because they are caved or surrounded by large caved areas or because they are completely inundated, the backfilling method to be employed is known as blind flushing. The operation consists of drilling bore holes to openings expected to exist according to available mine maps.

Since the flushing stream cannot be conducted underground horizontally to any place to be filled, the solids "ice dropped through a bore hole will accumulate at the bottom of the bore hole in a cone, the shape and extent of which depends on the size and consistency of the material and pitch of the strata. If the voids to be backfilled are inundated, the effectiveness of any backfilling operation will be further reduced, since the water standing in a bore hole exerts a definite resistance to the introduction of any solids. As a result, the solids accumulate in the form of a steep cone at the bottom of the vertical bore hole, supporting the roof of the chamber only over a comparatively small area.

Therefore, it is obvious that the controlled flushing is more highly desirable due to the greater effectiveness than the blind flushing. However, a very small percentage of the worked on area can be refilled by the controlled flushing" method of backfilling. However, heretofore, the blind flushing methods of backfilling were entirely unsatisfactory.

The slurry mixture which was run into an abandoned mine according to the prior processes, increased the hydrostatic pressure in the inundated mine because of the insertion of up to 25% of solid material into the cavity spaces which are already filled or partially filled with water. This entrance of the solid material creates a hydrostatic head which creates pressure in the already waterfilled mine which retards the flow of the solid material and causes the solids to settle out too rapidly, thereby building up a deposit or cone at the bottom of the bore hole or other underground entrance, Furthermore, the increase in the hydrostatic pressure causes an increase in pressure against the barrier pillars which separate the abandoned water-filled mine from a neighboring mine or mines which may be presently active, thereby causing the addition of pumping problems to the operating mine and also creating a hazardous situation which could result from the water in the abandoned mine being forced into the adjacent working mine. The present invention enables a blind flushing backfilling operation to be accomplished while obviating all the aforementioned hazards and problems.

The present method relates, in general, to the use of a slurry mixture of sand, clay, pulverized shale, rock, coal refuse material or other solids with a mixture of 30 to 60% water, which will be supplied to the area of the mine to be refilled by a new and unique apparatus which will permit directional flow of the slurry material to completely fill the cavity spaces presently filled or partially filled with water. The method of the present invention further provides for the removing of water from a filled or partially filled mine, thereby providing for equalization of hydrostatic pressure.

The directional flow orifice of the present invention which is attached to the bottom of the pipe extending through the bore hole prevents the solid material from penetrating through the water to the mine floor at the point where it enters from the surface. The flexible end of the directional flow orifice provides that slurry mixture which comes from the surface will enter the mine area in a substantially horizontal jet having a velocity sufficient to propel the slurry material to the extreme areas of the mine cavity. The current action of the water which is provided by the extraction pump assists the slurry mixtures movement in the proper direction by the movement of the water toward the pump intake which can be onehalf mile or more from the point of the slurry mixture insertion.

Other features of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose by way of example, the principles of the invention and the best mode which has been contemplated of applying those principles.

In the drawings:

FIGURE 1 is a sectional view of a mine cavity and the overlying strata in combination with a schematic showing of the apparatus utilized in the practice of the method of the present invention.

FIGURE 2 is a sectional view of a bore hole and the apparatus adapted to be inserted therein to accomplish the method of the present invention.

The present invention is directed to a method of backfilling an underground cavity, such as a coal mine or the like, comprising the steps of drilling at least two bore holes from the surface to the roof of the mine cavity, feeding a slurry of fill material and water from the surface to the mine cavity through one of said bore holes, variably directing the slurry to various parts of the mine cavity and pumping the displaced water from the mine cavity to the surface through the other of said bore holes. The apparatus for providing the variable direction flow of the slurry within the mine cavity is comprised of an elongated conduit adapted to be rotated about its longitudinal axis and an orifice pivotally secured to the lowermost end of said conduit.

Turning now to the drawings, we see that FIGURE 1 shows a sectional view of a mine cavity and the overlying strata along with a schematic showing of the various equipment necessary to perform the present invention. A source of material has been shown schematically in FIGURE 1. This material, which is used as the solid for the slurry mixture, may be most conveniently obtained from existing coal mine refuse dumps known as culm banks in the anthracite region and as gob piles in the bituminous mining area. The coal mining industry has been plaqued with the problem of waste removal for years and large unsightly culm banks and gob piles have grown up in various mining areas. These banks present a very hazardous situation since the banks may often become ignited and burn for years and years giving off noxious fumes which adversely affect the entire community. Another hazard encountered with these refuse dumps is the danger of a slide which could cause considerable property damage. Although coal mine refuse dumps are the most obvious source of the solid material for the slurry mixture, it is contemplated that other sources could readily be used.

The material from the refuse dumps or other sources is then transported by any suitable means to a crushing apparatus 12. The crushing apparatus 12 may be of .any suitable type for reducing the material to minus onefourth inch size particles. The particles may be stock piled subsequent to the crushing operation or transported directly to a mixing apparatus 14. A source of water 16 is also fed to the mixer 12 which may be a rotary type mixer wherein the water and the material are combined into a slurry which is then conducted by a conduit 18 to the entrance of the bore hole 20.

The bore hole extends through the upper layer of soil and gravel 22 through the rock strata 24 and intersects the roof of the mine cavity 26. The mine cavity 26 which is to be filled with the slurry material is separated from adjacent 'rnine cavities 28 by means of a barrier pillar 30. As can readily be seen from the drawing, the barrier pillar 30 only provides support for the area 32 immediately above the pillar and outlined by dotted lines. The remainder of the rock strata and surface layer is completely unsupported and frequently the unsupported rock strata crumbles in an area designated 34 with the subq e caving of the surface at 36. Such cave-ins cause .4 considerable surface property damage by causing buildings to crack and collapse with the attendant danger to the inhabitants of these buildings.

A pipe or conduit 38 is inserted through the bore hole 20 and is adapted to guide the slurry from the surface to the mine cavity. A second bore 40 is drilled through the surface layer and the rock strata to a portion of the mine cavity remote from the bore 20. A pumping means 42 as shown schematically in FIGURE 1 is inserted into the bore hole 40 .and provides for lifting the mine water from the cavity to the surface. When the water reaches the surface, a portion of the water is diverted through conduit 16 to provide the necessary water for making the slurry and the remainder is allowed to run off through the conduit 44.

Turning now to FIGURE 2, we see the details of the inlet conduit and the directional flow orifice. The conduit 38 is provided at the lowermost end thereof with a buffer ring or flange which facilitates guiding the conduit through the bore hole. The uppermost end of the conduit which extends above the surface of the ground is provided with a ring gear 48 secured thereto by an suitable means. The ring gear 48 meshes with a pinion gear 50 which is is secured to the driven shaft 52 of any suitable drive means 54, such as an electric motor or the like. The conduit is provided with a longitudinal rib or marking means 56 which coincides with the direction in which the slurry will be directed when it passes through the adjustable orifice at the bottom of the conduit. By rotating the motor 54, the gear 50 will turn the shaft and the entire conduit assembly so as to control the direction of flow 0f the slurry as it leaves the conduit. The nozzle means is comprised of a scoop-like member 58 pivotally secured to the lower end of the conduit at 60. The nozzle scoop 58 is held in its solid line posiion by means of a pin 62 which extends through aligned openings in a flanged 64 on the end of the conduit and a flange 66 on the nozzle member. A wire or cable 68 is secured to the pin 62 and extends upwardly tothe surface so that upon applying an upward force on the wire 68, the pin 62 will be withdrawn from the hole in the flange 66 allowing the nozzle or spout 58 to be pivoted to the dot-dash line position by means of the spring 70 which is wrapped around the pivot 60 and bears against the conduit and the orifice. When the conduit is being lowered through the bore hole 20, the orifice or scoop 58 will be retained in the solid line position by means of the pin 62 and once the lower end of the conduit protrudes into the mine cavity, the pin may be released to allow the orifice 0r scoop 58 to be pivoted to the correct position. In the dot-dash position, the slurry which is fed downwardly through the conduit 38 will be deflected in a generally horizontal direction into the mine cavity. When it is desired to remove the conduit, the orifice or scoop 58 will merely pivot downwardly against the action of the spring 70 as the conduit is pulled upwardly through the bore hole 20.

It is contemplated, of course, that the conduit may be comprised of various sections joined together similar to the pipe inserted into an oil well and that the guide strip or marking 56 on each pipe would be aligned as each additional section of conduit is secured to the main conduit. Some attempts have been made in the past to use an elbow at the bottom of a pipe inserted through a bore hole into a mined out area, but in order to use an elbow, the diameter of the pipe would have to be much less than the size of the bore hole, thereby decreasing the capacity of the pipe used in the bore hole. The present invention allows for a large diameter pipe to be inserted into the bore hole with the subsequent spring actuation of the guide orifice into the proper position once the lower end of the conduit penetrates the mine cavity. The springblased feature of the guide orifice also precludes any jam, up at the mouth of the conduit since any excessive buildup of the slurry at this point would cause the spring 70 to yield and automatically clear the blockage.

The operation of the present method should be obvious from the foregoing description but the details of 'an exemplary backfilling operation will now be set forth to more clearly define the method. The bore hole 20 is ordinarily placed within 300 feet of an existing barrier pillar and the initial filling of the mined out area may be directed the barrier pillar which will be thereby strengthened by the slurry mixture. Distances of more than 300 feet from the barrier pillar should not be attempted as the flow of water at the bore hole entrance of the deep well pump will normally be in the opposite direction, the effect of the velocity or hydrostatic head of the slurry mixture will begin to lose its effect at distances greater than 300 feet when the current flow of the mine, that is partially or totally inundated, is in the opposite direction toward the deep well pump.

When sufllcient tonnage or cubic yardage of material, as determined by a study of the mining maps has been moved into place to adequately reinforce the barrier pillar in that direction, the orifice should then be turned by the surface control so that the orifice or nozzle is now pointing in the direction toward the deep well pump intake, which may be a thousand feet to five thousand feet from the point of slurry intake.

This new method balances the hydrostatic pressure of a mine that is partially or totally inundated by removing, by means of pumping, an amount of water equal in cubic feet per minute to that of the slurry mixture which is being inserted in the intake bore hole. The purpose of this balancing of the hydrostatic pressure in a mine is to prevent excess pressure from developing against the barrier pillar which is between a neighboring mine and the mine to be backfilled by the slurry mixture. If the mined out area is partially or totally inundated, the amount of Water in the slurry mixture may be much less than that which would be used in a dry mine in which there would be no water to assist in transporting the solids in the slurry mixture to a point near the bottom of the intake of the deep well pump.

The slurry mixture introduced by the proposed method will travel a much greater distance than solids or slurries previously introduced into a mine because of the controlled directional fiow provided by this method and because of the continuous current flowing in the direction of the pump which may be a thousand to five thousand feet or more from the point of the introduction of the slurry mixture into the mine to be backfilled. The solids in the slurry mixture will settle out by sedimentation according to their sizes and specific gravities. As a bottom of slurry builds up on the mine floor, the material deposited there will have an effect similar to that of ball bearings in moving the additional material as it settles out from the flow from the intake to a point where the deep Well pump is drawing it by means of the current which it sets up as it Withdraws the water from the inundated or partially inundated or dry mine. The ball bearing effect is commonly known as saltation, common terminology for movement of sediment along the surface of previously deposited sediment or fine material. If the slurry filling is being inserted into a dry mine, the deep well pump must be run intermittently or a pump of smaller capacity to handle the quantity of Water added by the slurry mixture due to the fact that the amount of water entering the mine will be less than a larger pump would ordinarily handle in the case where there is a balance flow between the intake of the slurry and the outlet caused by the pumping process.

The cavity space in the worked out mine should be determined in advance so the number of cubic yards of solid material needed can be determined. A belt scale device could be placed ahead of the rotary mixer so that an accurate record may be kept of the tons of solids material. A colored substance should be inserted daily to act as a tracer to determine the travel time from the slurry intake pipe to the surface at the deep well pumping location.

When the amount of solid material introduced through the slurry mixture is equal to the cavity space previously determined or when the deep well pump is beginning to withdraw some of the solids from the slurry mixture, a postponement of operation should be made for a period of approximately two weeks to permit the liquids from the slurry to drain to the low point in the mine or where the intake of the deep well pump is located. After a two week quiescent period, the slurry mixture should again be introduced into the mine and the deep well pump should be run at intervals to maintain the flow of water at the low point. Thus, there will be no hydrostatic backlash or buildup from the water near the intake end of the deep well pump. This secondary filling, after the quiescent period, should provide an additional five to ten percent of solids. The previously inserted slurry mixture will have settled in the water 'leaving a solid mass which in turn will cement itself and provide permanent support for the surface area which was previously undergoing subsidence. A flocculent may be added to the slurry prior to feeding the slurry into the mine cavity which will aid in expediting the cementing operation of the material in the mine.

In addition to providing a physical support for the rock strata and surface layers immediately above the mine cavity, the backfill will also provide a covering of the acid producing features of an open top and bottom rock or slate covering, usually found above and below the coal veins. This covering of the acid producing materials will prevent the action of the oxygen and acid producing materials in the mine from contaminating whatever water may get into the mine from the surface or from underground sources. Thus, the present method will decrease the possi bility of water becoming polluted to the level that it is now when it flows or is pumped from an abandoned or partially abandoned mine.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A method for backfilling an underground mine cavity requiring blind flushing comprising:

(a) drilling at least two spaced bore holes from the surface through the roof of the mine cavity to be filled,

(b) providing a conduit having a variable direction orifice secured thereto and dimensioned to be capable of insertion throught one of said bore holes,

(c) inserting said conduit and variable direction orifice into said one of said bore holes,

((1) mixing a slurry of solid material and water,

(e) introducing said slurry into said mine cavity through said conduit,

(f) adjusting said variable direction orifice so as to direct the flow of slurry material toward another bore hole, and

(g) pumping excess water in said mine cavity to the surface through said another bore hole.

2. A method for backfilling an underground mine cavity as set forth in claim 1 further comprising intially adjusting said variable direction orifice to direct the flow of slurry in a direction away from the bore hole through which the water is pumped out of the mine cavity.

3. A conduit for introducing material into a blind cavity comprising a substantially hollow cylindrical conduit adapted to extend through an opening into said blind cavity, first means secured to one end of said conduit means externally of said cavity for rotating said conduit means about its longitudinal axis and second means secured to the opposite end of said conduit within said blind cavity for diverting the flow of material at substantially right angles to the direction of flow of the material through said conduit, said second means being comprised of a scoop-shaped orifice member pivotally secured to the lower end of said conduit, latch means adapted to hold said orifice member in axially aligned relation with said conduit during, the insertion of said conduit into said cavity and spring means adapted to bias said orifice member to a laterally oflset position with respect to the axis of said conduit upon release of said latch means.

References Cited UNITED STATES PATENTS JACOB SHAPIRO, Primary Examiner.

U.S. Cl. X.R. 6163 

